The lifespans of gorillas in a particular zoo are normally distributed. The average gorilla lives $20.8$ years; the standard deviation is $3.1$ years. Use the empirical rule $(68-95-99.7\%)$ to estimate the probability of a gorilla living less than $23.9$ years.
Explanation: The probability of a particular gorilla living less than $23.9$ years is ${68\%} + {16\%}$, or $84\%$.